Mostly used two of my USB chargers I also use for my tablet and my smartphone. 5 volts, 1 ampere, nothing special. It worked for years. Also used a USB power bank a few times... But that stopped working years ago. After several months of non use, I tried to charge the controllers again but they seemed to be dead. They were not showing any sign of life. But after connecting them to one of those chargers and pressing the PS button they at least were flashing the Led. So the USB port, the cable and the charger seemed to be okay.
I even opened one controller, and charged the battery directly via a bench top power supply. The battery was outputting 0 volts before, but was able to be charged. It was also able to keep the charge. So the battery seemed to be fine.
The solution that finally worked: bought a used original charging station. Placing a controller in the charger starts the charging process and the Led on the controller turns yellow...
And the reason for this weird behavior? I have no clue. My current theory: perhaps tolerance issues due to aging in some electrical components?